1. Field of Invention
This invention relates to molds that contain a mold insert.
2. Description of Related Art
Magnetic rolls can be made by injection molding a plastic resin highly filled with ferrite particles into a cylindrical mold. The mold includes a body having a cylindrical opening that extends through the body. The mold typically also includes a mold insert to accommodate the abrasive wear caused by the material used to make the magnetic roller. The mold insert is positioned at least partially against the surface of the cylindrical opening in the body. The inner surface of the mold insert is adapted to conform to at least a portion of the periphery of the magnetic roll. The mold inserts are replaceable so that a worn insert may be replaced with a new insert.
The ferrite-filled plastic material used to make magnetic members is both abrasive and corrosive. Thus, a mold insert is required to be durable and exhibit the required thermal and magnetic characteristics. Mold inserts are typically made of any suitable durable material. Preferably, mold inserts are made of a non-magnetic metal, for example beryllium-copper (Bexe2x80x94Cu).
Mold inserts are prone to chemical attack and abrasive wear. Thus, mold inserts need to be replaced frequently. In a typical injection molding apparatus, a Bexe2x80x94Cu mold insert needs to be replaced after forming about 25,000 magnetic members. A Bexe2x80x94Cu mold insert costs nearly $10,000. The frequency of replacement of mold inserts, combined with the high cost of mold inserts, increases the overall cost of producing magnetic members using an injection molding process.
Attempts have been made to coat mold inserts with a hard coating to prevent wearing of the mold inserts. Several hard coatings have been tried, but have not successfully prevented wearing of the mold inserts for several reasons. Ferrite particles in the mold material mechanically attack and wear away many coatings quickly and easily. After the coating is mechanically removed, the mold insert is susceptible to chemical and mechanical attack.
This invention provides mold insert coating structures that protect mold inserts from chemical attack and abrasive wear of mold materials, and methods for coating mold inserts with the coating.
This invention separately provides mold insert coating structures that protect mold inserts form chemical attack and abrasive wear over a long period of time, and methods for coating mold inserts with the coating.
This invention separately provides mold insert coating structures that reduce the expense of injection molding magnetic members by reducing the number of times mold inserts need to be replaced, and methods for coating mold inserts with the coating.
In various exemplary embodiments of the coating structures and methods according to this invention, a removeable mold insert is provided in a mold. The mold insert includes a Bexe2x80x94Cu mold insert. An electroless nickel layer is formed on or over the Bexe2x80x94Cu mold insert. A layer of chromium nitride is formed on or over the electroless nickel layer. The electroless nickel layer and the chromium nitride layer reduce the effects of corrosive wear and chemical attack on the mold material and the Bexe2x80x94Cu mold insert.
These and other features and advantages of the invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the methods according to this invention.